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Summary of Significant Accounting Policies Summary of Significant Accounting Policies (Trust Assets) (Details) $ in Thousands | Dec. 31, 2018 USD ($) trust_accounts | Dec. 31, 2017 USD ($) trust_accounts
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Organization, Consolidation and Presentation of Financial Statements [Abstract] |  |
Number of Trust Accounts managed or administered | trust_accounts | 1,141 | 1,119
Value of Trust Accounts | $ | $ 1,129,600 | $ 997,790

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